1. Field of the Invention
The present invention relates to a thermal head and a printer.
2. Description of the Related Art
There have been conventionally known a thermal head which is used in a thermal printer often mounted to a portable information equipment terminal typified by a compact hand-held terminal, and which is used to perform printing on a thermal recording medium based on printing data with the aid of selective driving of a plurality of heating elements (for example, see JP 06-166197 A).
In terms of an increase in efficiency of the thermal head, there is a method of forming a heat insulating layer below a heating portion of a heating resistor. By formation of the heat insulating layer below the heating portion, of an amount of heat generated in the heating resistor, an amount of upper-transferred heat which is transferred to an abrasion resistance layer formed above the heating portion becomes larger than an amount of lower-transferred heat which is transferred to a heat storage layer formed below the heating portion, and hence energy efficiency required during printing can be sufficiently obtained. In the thermal head described in JP 06-166197 A, a hollow portion is provided in a layer below the heating portion of the heating resistor, and this hollow portion functions as a hollow heat insulating layer. Thus, the amount of upper-transferred heat becomes larger than the amount of lower-transferred heat, and the energy efficiency is increased.
Further, in a printer in which a thermal head is installed, thermal paper is pressed, with a predetermined pressing force, against a head portion of a surface of the abrasion resistance layer formed above the heating portion. Therefore, the thermal head is required to have heat generation efficiency for improving printing quality as described above, and required to have strength for withstanding the pressing force of the platen roller.
However, in the hollow heat insulating layer of the thermal head described in Patent Document 1, a center position of the hollow portion substantially corresponds to a center position of the heat generating portion, the hollow heat insulating layer having a size with which the heat generating portion is contained in a region of the hollow portion. Therefore, when an external load is applied to the heat generating portion, deflection at a central portion of the heat storage layer becomes large. Particularly, there is a risk that deflection of the heat storage layer becomes excessive in the case of a sheet jam or the like, whereby the heat storage layer is broken. Further, there is a risk that, when a pressing force of the platen roller causes the heat storage layer to be deflected, a contact state between the thermal paper and the head portion is deteriorated so as to decrease a contact pressure, and it becomes difficult to be transfer heat to the thermal paper.